Toxins

Toxins

• Toxic substances produced by biological systems (plants, animals, fungi, or bacteria).

Toxic Compounds from Plants

• Concentration of toxic chemicals in plants may vary:
  • Different parts of the plant may contain different concentrations of a chemical.
  • Peak concentrations of bioactive compounds are often found at different times.
  • Age and season influence the synthesis of some chemicals.
  • Genetic differences within a species alter the ability of plants to synthesize a chemical.
• Plants have developed various defenses (from viruses, bacteria, fungi, and animals) including:
  • Synthesis of antimicrobial chemicals.
  • Chemicals designed to repel animals by various means.

Skin Irritations

• Examples:
  • Poison Ivy
  • Poison Oak
  • Poison Sumac

Urushiol

• Poison ivy, poison oak, and poison sumac contain an irritating, oily sap called urushiol.
• Urushiol is found in all parts of the plants (leaves, stems, and roots), even when the plants are dead.
• Herbarium specimens 100 years old have been known to cause dermatitis.
• Urushiol triggers an allergic reaction when it comes into contact with the skin, resulting in an itchy rash that can appear within hours of exposure or three to five days later.
• Inhaled urushiol can cause a very serious allergic reaction.
• An allergic reaction to a poison plant cannot be cured, but the symptoms can be treated (calamine lotion).
• Urushiol is also present in mango leaves and stems.
• Contact with oils in mango leaves, stems, and sap during ripening season can cause dermatitis and anaphylaxis in susceptible individuals.

Giant Hogweed (Heracleum mantegazzianum)

• One plant produces 20,000 seeds every growing season.
• It is a native of the Eurasia area, but spread into Europe and United States.
• It is a biennial and it tolerates even the coldest climates.
• It can grow to 15 feet tall and has been planted for ornamental purposes.
• The furocoumarins found in the white sap can cause severe burns, scars, and temporary and even permanent blindness when it comes in contact with skin or eyes.
• Giant hogweed is on the federal and Ohio noxious weed lists making it unlawful to propagate, sell, or transport (due to its ability to crowd out native plants and because of its potential human health hazard).

Exposure to Urushiol

• Poison ivy, poison oak, and poison sumac are three of the most common causes of allergic contact dermatitis in North America.
• Some experts estimate that 8 out of 10 people are sensitive to the urushiol found in these plants, although the degree of sensitivity varies.
• Cases of poison plant allergy occur most frequently during the spring, summer, and early fall when people spend more time outdoors.
• Urushiol is easily transferred from one object to another by plant oil.
• It is not spread through blister fluids.

Cardioactive Glycosides

• Several different families of plants contain species with cardioactive glycosides, the best known of which is Digitalis purpurea (foxglove, Scrophulariaceae).
• Foxglove poisoning usually occurs from sucking the flowers or eating the seeds, stems, or leaves of the foxglove plant.
• Digitalis glycosides are a group of chemically related compounds isolated primarily from the purple and white foxglove plants.
• Digoxin toxicity is common and potentially fatal.

Digoxin Mechanism of Action

• High doses of a digitalis glycoside inhibit the Na/K pump that lead to:
  • decrease of intracellular [K^+], a build up of extracellular [K^+]
  • rise of intracellular [Na^+]
  • rise of intracellular [Ca^{2+}] due to the Na/Ca exchange mechanism

Oleander

• Oleander is a poisonous perennial plant that grows in Ohio.
• It has smooth, thin leaves with red-purple flowers that bloom throughout the Summer and produces seeds in the Fall.
• It loves the sun and can tolerate drought.
• All parts of the plant are highly toxic to humans and life-stock animals.

Cardenolide Glycosides

• Oleanders contain a toxin called Cardenolide glycosides.
• The toxin is mostly contained in the sap which is clear to slightly milky colored, and sticky.
• When ingested in certain quantities, this toxin can cause harm and possibly death.
• Cardenolide glycosides are Na+/K+ -arresting by similar mechanism as digitalis glycosides.

Nervous System

• Historically, some of the most useful drugs have been plant- derived chemicals that act on the nervous system.
• However, some unintended serious neurotoxic syndromes may result from ingestion of certain plants.

Parasympathetic Block

• The belladonna alkaloids (atropine, L-hyoscyamine, and scopolamine) are found in several genera of Solanaceae, the nightshade family.
• The plants are widely distributed.
  • Datura stramonium (jimson weed) is native to India and contains primarily scopolamine
  • Hyoscyamus niger (henbane) native to Europe and Duboisia myoporoides
  • (pituri) in Australia contain primarily L-hyoscyamine
  • Atropa belladonna (deadly nightshade), also native to Europe, contains atropine.

Effect of Belladonna Alkaloids

• Scopolamine, L-hyoscyamine and atropine affect CNS by blocking muscarinic receptors.
• The effects of modest doses:
  • tachycardia
  • dry mouth
  • dilated pupils
  • decreased gastrointestinal motility
• Large doses affect the central nervous system with confusion, bizarre behavior, hallucinations, and subsequent amnesia.
• Deaths are rare, although recovery may take several days.

Poison Hemlock

• Poison Hemlock (Conium maculatum) is a poisonous member of the Umbrellacea family (the same as Hogweed).
• Currently, it can be found all over Ohio.
• It can grow up to 7 feet tall and can survive in many different soil types including abandoned fields, roadsides, and wet soils.
• It has been planted in many areas as an ornamental despite its severe toxicity to humans and animals.
• It has a strong noxious smell.

Piperidine (Nicotinic) Alkaloids from Hemlock

• Piperidine (nicotinic) alkaloids in Conium include coniine (2-propylpiperidine) and coniceine.
• During the first year of growth, the plant alkaloid content tends to be lower.
• In the second year - alkaloids content is approximately 1% in all plant parts.
• Coniine progressively increases in flowers and fruits, while coniceine decreases during plant maturation.
• Poison-hemlock is acutely toxic to people and animals, with symptoms appearing 20 minutes to three hours after ingestion.
• The typical symptoms:
  • dilation of the pupils
  • dizziness
  • trembling followed by slowing of the heartbeat
  • paralysis of the CNS
  • muscle paralysis
  • death due to respiratory failure
• No antidote is available.
• Coniine increases the permeability of the motoneuron membrane to Na+ ions.
• Coniceine and coniine are teratogenic alkaloids.

Strychnine

• The primary natural source of strychnine is the plant Strychnos nux-vomica found in southern Asia (India, Sri Lanka, and East Indies) and Australia.
• Strychnine is a strong poison.
• Strychnine inhibits competitively and reversibly the action of neurotransmitter glycine in the spinal cord and medulla.
• Due to this action, muscles throughout the body have severe, painful spasms.
• Even though the person’s consciousness or thinking are not affected at first (except that the person is very excitable and in pain), eventually the muscles tire and the person can’t breathe.

Water Hemlock

• The parsley family of plants (Apiaceae) contains some of the most edible (e.g., carrots) and some of the most poisonous plants in the northern hemisphere.
• The fleshy tubers of water hemlock (Cicuta maculata) may be mistaken for other edible wild tubers.
• A single tuber may cause fatal poisoning, characterized by convulsions.
• Toxic cicutoxin (a C17- polyacetylene) binds to GABA -gated chloride channels and this may play a role in the acute neurotoxicity.

Fungal Toxins

• The fungus Amanita muscaria (fly agaric) got its name from its poisonous actions on flies.
• Poisoning from this woodland mushroom is due to the content of the excitatory amino acid, ibotenic acid (isoxazole amino acid), and to its derivative, muscimol.
• The effects are CNS depression, ataxia, hysteria, and hallucinations.
• The content of ibotenic acid varies with the time of year; more has been reported in summer than in fall.
• Several other genera of fungi have hallucinogenic actions, notably Psilocybe, containing the indoles: psilocin and psilocybin.

Protein Synthesis Inhibition

• Castor bean (Ricinus communis) is a member of the family Euphorbiaceae, which contains several genera that produce toxic chemicals.
• If the seeds are eaten, children and adults experience no marked symptoms of poisoning for several days.
• In this interval there is some loss of appetite, with nausea, vomiting, and diarrhea developing gradually.
• With fatal doses the gastroenteritis becomes severe, with persistent vomiting, bloody diarrhea, and jaundice.
• The fatal dose for a child can be 1-3 seeds; it may be as low as 4-8 seeds for an adult.
• Death occurs in 6–8 days.
• Variety of plants produce cytotoxic proteins related to ricin (structure and function).
• They inhibit protein synthesis by specifically and irreversibly inactivating eukaryotic 28S rRNA.
• These "ribosome-inactivating proteins" (RIPs) are divided into two types.
  • Type 1 RIPs - less poisonous; wheat and barley
  • Type 2 RIPs, the most potent cytotoxins in nature, the castor bean plant seeds
• Just a single ricin molecule that enters the cytosol can inactivate over 1500 ribosomes per minute killing the cell.

Botulinum Toxin (BT)

• Botulinum toxin (BT) is a potent neurotoxin that is produced by the gram- positive, spore-forming, anaerobic bacterium, Clostridum botulinum.
• BT’s molecular mode of action includes extracellular binding to glycoprotein structures on cholinergic nerve terminals and intracellular blockade of the acetylcholine secretion.
• LD_{50} = 0.00001 mg/kg
• BT affects the spinal stretch reflex by blockade of muscle fibers and muscle tone without affecting muscle strength (reflex inhibition).
• BT also blocks efferent autonomic fibers to smooth muscles and to exocrine glands.
• Direct central nervous system effects are not observed, since BT does not cross the blood-brain-barrier.

ANIMAL TOXINS

• Venomous and poisonous animals are widely distributed throughout the animal kingdom.
• Venomous animals are capable of producing a poison in a highly developed exocrine gland or group of cells and can deliver their toxin during a biting or stinging act.
• The venom is the sum of all natural venomous substances produced in the animal.
• Animal venom may play a role in offense, as in the capture and digestion of food, in the animal’s defense, as in protection against predators or aggressors, or in both functions.

Functions of Venoms

• In the snake, the venom provides a prey -getting mechanism.
  • Its secondary function is its defensive status.
• In venomous spiders, toxin is used to immobilize the prey before the extraction of hemolymph and body fluids.
  • The same can be said for the scorpions, although they do use their venom in defense.
• Fish, stingrays, and frogs use the venom apparatus in the animal’s defense.

PROPERTIES OF ANIMAL TOXINS

• Venoms are very complex, containing:
  • polypeptides
  • high- and low-molecular-weight proteins
  • amines
  • lipids, including steroids
  • aminopolysaccharides
  • quinones
  • glucosides
  • free amino acids
  • serotonin
  • histamine
  • other substances
• Some venoms may consist of more than a hundred proteins.

Bioavailability of Venoms

• The bioavailability of a venom is determined by:
  • its composition
  • molecular size
  • amount or concentration gradient
  • solubility
  • degree of ionization
  • the rate of blood flow into that tissue
  • the properties of the affected surface
• The venom can be absorbed by active or passive transport, facilitated diffusion, or pinocytosis, among other physiologic mechanisms.
• The site of action and metabolism of venom is dependent on its diffusion and partitioning along the gradient between the plasma and the tissues where the components are deposited.

Arthropods

• Out of 25 orders of arthropods, only about 10 orders are of significant venomous or poisonous importance:
  • arachnids (scorpions, spiders, mites, and ticks)
  • myriapods (centipedes and millipedes)
  • insects (water bugs, assassin bugs, and wheel bugs)
  • beetles (blister beetles)
  • Lepidoptera (butterflies, moths, and caterpillars)
  • Hymenoptera (ants, bees, and wasps)
• In Mexico, parts of Central and South America, North Africa, and India, deaths from scorpion stings, for instance, exceed 3,000 a year.
• Spider bites probably do not account for more than 10 deaths a year worldwide.

Scorpions

• Scorpions spend the daylight hours under cover or in burrows.
• They emerge at night to ambush other arthropods or even small rodents, capture them with their pincers, sting and paralyze them, or tear them apart and digest their body fluids.
• Many scorpion venoms contain low-molecular-weight proteins, peptides, amino acids, nucleotides, and salts, among other components.
• The neurotoxic fractions are generally classified on the basis of their molecular size:
  • the short-chain toxins being composed of 20–40 amino acid residues appear to affect potassium or chloride channels
  • the long-chain toxins have 58–76 amino acid residues affect mainly the sodium channels.

Effects of Scorpion Envenomation

• The symptoms and signs of scorpion envenomation differ considerably depending on the species.
  • Initial localized pain, swelling, tenderness, and mild paresthesia (tingling)
  • Tachycardia and hypertension - within 45 minutes
  • Respiratory and heart rates are increased and by 90 minutes the person appear ill
  • The respiratory distress may proceed to respiratory paralysis
  • Excessive salivation
  • Slurring of speech and convulsions
• If death does not occur, the child usually becomes asymptomatic within 36–48 hours, most adults are asymptomatic within 12 hours, but may complain of generalized weakness for 24 hours or more.

Spiders

• Of about 30,000 species, at least 200 have been implicated in significant bites on humans.
• Spider venoms are complex mixtures of low-molecular-weight components, including inorganic ions and salts, acids, amino acids, biogenic amines and neurotransmitters, and polypeptide toxins.
• The acylpolyamines are composed of a hydrophobic aromatic carboxylic acid linked to a lateral chain of one to nine aminopropyl, aminobutyl, or aminopentyl units.

Effects of Spider Toxins

• The acylpolyamines are voltage-dependent open-channel blockers (sodium, calcium, and potassium channels) and/or blockers of the ion channel associated with glutamate receptors.
• The acylpolyamines also act on nicotinic acetylcholine receptors.
• The acylpolyamines possess insecticidal activity and induce fast insect paralysis.
• Polypeptide toxins include the calcium channel blockers, pore-forming peptides, and enzymes.

Latrodectus Species (Widow Spiders)

• Although both male and female widow spiders are venomous, only the female has fangs that are large and strong enough to penetrate the human skin.
• Mature Latrodectus mactans females range in body length from 10 to 18 mm, whereas males range from 3 to 5 mm.
• The latrotoxins, a family of high-molecular-weight proteins that are found in Latrodectus venoms, target different classes of animals including vertebrates, insects, and crustaceans.
• The toxins are synthesized as large precursors containing around 1000 amino acid residues (around 132–156 kDa) that undergo proteolytic processing to 110–130 kDa and activation in the lumen of the venom gland.

Effect of Latrotoxins

• All latrotoxins stimulate massive release of neurotransmitters after binding to specific neuronal receptors.
• α-Latrotoxin exerts its toxic effects by increasing intracellular [Ca^{2+}].

Black Widow Bites

• Bites by the black widow are described as sharp and pinprick like, followed by a dull, occasionally numbing pain in the affected extremity and by pain and cramps in one or several of the large muscle masses.
• Muscle twitching frequently can be seen within 30 minutes of the bite.
• Pain in the low back, thighs, or abdomen is a common complaint, and rigidity of the abdominal muscles is seen in most cases in which envenomation has been severe.

Loxosceles Species (Brown or Violin Spiders)

• These primitive spiders are variously known in North America as the fiddle- back spider or the brown recluse.
• There are over 100 species of Loxosceles.
• This spider has six eyes grouped in three dyads.
• Females average 8–12 mm in body length, whereas males average 6–10 mm.
• Both males and females are venomous.
• The venom of Loxosceles spiders contains phospholipase, protease, esterase, collagenase, hyaluronidase, deoxyribonuclease, ribonuclease, dipeptides, dermonecrosis factors, and sphingomyelinase D.
• The venom has coagulation and vasoconstriction properties and it causes selective vascular endothelial damage.

CHILOPODA (CENTIPEDES)

• Found worldwide, these elongated, many-segmented brownish-yellow arthropods have a pair of walking legs on most segments, and they are fast moving, secretive, and nocturnal.
• They feed on other arthropods and even small vertebrates and birds.
• The first pair of legs behind the head is modified into poison jaws.
• Centipedes range in length from 0.3 to 30 cm.
• In the United States, the prevalent biting genus is a Scolopendra species.

Centipede Venoms

• Centipede venoms contain a heat-labile cardiotoxic protein that in humans produces changes associated with acetylcholine release.
• The bite produces two tiny punctures, sharp pain, immediate bleeding, redness, and swelling often lasting for 24 hours.
• In the most severe cases can cause mental disturbances.

Theraphosidae Species (Tarantulas)

• True tarantulas are members of the family Theraphosidae and there are around 800 species that are distributed worldwide, but especially in tropical or semitropical regions.
• The venom of tarantulas found in the United States is not considered dangerous but may cause allergic reactions.
• In humans, reported bites elicit mild-to- severe local pain, strong itching, and tenderness that may last for several hours.
• In more severe cases, strong cramps and muscular spasms lasting up to several hours may be observed.

Lepidoptera (Caterpillars, Moths, and Butterflies)

• The urticating hairs (setae) of caterpillars are effective defensive weapons that protect some species from predators.
• The toxic material found in the venom glands contains aristolochic acids, cardenolides, kallikrein (serine proteases), and histamine among other substances.
• The spicules of Thaumetopoea pityocampa contain a 28-kDa toxin called thaumetopoein, which is a strong dermal irritant and highly allergenic peptide.
• In some parts of the world the stings of several species of Lepidoptera give rise to a bleeding, sometimes fatal.

Poison Dart Frog

• Poison dart frogs are the members of the Dendrobatidae family.
• Dendrobatids include some of the most toxic animals on Earth.
• The two-inch-long golden poison dart frog has enough venom (batrachotoxin) to kill 10 grown men.
• Batrachotoxin acts on the membrane by specifically increasing Na+ permeability.
• Scientists believe that frogs gain their poison from a specific arthropod and other insects that they eat in the wild.
  • These insects most likely acquire the poison from their plant diet.

Tetrodotoxin

• tetrodotoxin is an extremely potent poison (toxin) found mainly in the skin, liver and sex organs (gonads) of some fish, such as puffer fish, globefish, and toadfish and in some amphibian, octopus, and shellfish species.
• Human poisonings occur when the fish is improperly prepared and eaten.
• After ingestion, this poison reaches the voltage-gated Na+ channels of motor neurons.
• Interaction of tetrodotoxin with this target results in blockade of Na+ channels, inhibition of the activity of motor neurons, and ultimately skeletal muscle paralysis.
• No repair mechanisms can prevent the onset of such toxicity.

Poisonous Fish

• Boxfish and trunkfish are closely related to pufferfish.
  • The Hawaiian boxfish in particular excretes a toxin called ostracitoxin or pahutoxin that is known to breakdown or destroy red blood cells.
• Stonefish:
  • They reside in the Indo-Pacific region and northern Australia.
  • They deliver their venom through a row of spines on their back that can be extended when threatened (or stepped on).
  • A sting from one of these fish can cause excruciating pain, rapid swelling, tissue death, muscle weakness, temporary paralysis, and in very rare cases death.

REPTILES: Snakes

• Of the approximately 2700 known species of snakes, about 15% are considered to be venomous.
• In general, the anatomical structure of fangs makes it nearly impossible for snakes to chew their prey.
• The distinct curvature of the fangs is not only engineered for puncturing skin and delivering venom, but also for swallowing whole prey as well.
• The venom gland is positioned at the base of a long (∼30 mm) hollow retractable fang.
• Muscle pressure on the gland determines the amount of venom released.

Snake Bites

• Toxin delivery via venom exposure is the primary mechanism by which snakes immobilize and kill their prey.
• Toxin type and specificity is dependent on the species; most venom comprises of complex networks of toxins that affect variable organ systems and interact with one another increasing the overall potency.
• It is estimated that there are over 2.5 million snakebites annually, and that over 100,000 victims will die.

Snake Venoms Composition

• Snake Venoms are complex mixtures
  • Proteins
    • Enzymes
      • Acetylcholinesterases (AChE)
      • Aminotransferases
      • ADPases and ATPases
      • β-glucosaminidase
      • CVF
      • Catalases
      • Phosphoesterases
      • Phosphomonoesterases
      • Phosphodiesterases
      • PLA2 (synovial and pancreatic-type)
      • Hyaluronidases
      • L-amino acid oxidases (LAO)
      • NAD nucleosidases
      • Aspartic/Thiol proteases (traces)
    • Nonenzymatic
      • C protein activators
      • Growth factors (NGF, VEGF)
      • Inhibitors of the prothrombinase complex formation
      • Lectins (C-type lectins, galactose-binding lectins)
      • Precursors of bioactive peptides
      • von Willebrand factor-binding proteins
      • Platelet GPIb-binding proteins
      • CRISPS
  • Peptides
    • Toxic (cytotoxic, cardiotoxic, myotoxic, neurotoxic)
    • Enzymatic inhibitors
    • Disintegrins
      • Non-RGD
      • S-RGD
    • Natriuretic
    • Bradykinin potentiators
      • ACE inhibitors (ACEI)
    • Prokinecitin-like
    • CRISPS
    • Waglerins
  • Organic compounds with low molecular mass
    • Biogenic amines
      • Serotonin, histamine
    • Amino acids
    • Carbohydrates
    • Citrate
    • Nucleosides
  • Inorganic compounds
    • Calcium
    • Cobalt
    • Cooper
    • Iron
    • Phosphorus
    • Potassium
    • Magnesium
    • Manganese
    • Sodium
    • Zinc

Snake Venoms Composition (cont.)

• Group toxin components: neurotoxins, coagulants, hemorrhagins, hemolytics, myotoxins, cytotoxins, and nephrotoxins.

• Neurotoxins produce neuromuscular paralysis : to facial muscle paralysis, inability to swallow; paralysis of larger muscle groups; and finally paralysis of respiratory muscles causing death by asphyxiation.

• Coagulants may directly inhibit normal clotting at several places in the clotting cascade, some venom components may damage the endothelial lining of blood vessels leading to hemorrhage.

• Myotoxins can directly impact muscle contraction leading to paralysis.

• Cytotoxic agents have proteolytic or necrotic properties leading to the break down of tissue. Typical signs include massive swelling, pain, discoloration, blistering, bruising, and wound weeping.

• Sarafotoxins (found only in burrowing asps of Afro-Arabia) cause coronary artery constriction that can lead to reduced coronary blood flow, angina, and myocardial infarction.

• Nephrotoxins can cause direct damage to kidney structures leading to bleeding, damage of the nephron, tissue oxygen deprivation, and renal failure.

Enzymes in the Snake Venom

• At least 26 different enzymes have been isolated from snake venoms, which are comprised of amino acid sequences (150–1500).
• Proteolytic enzymes that catalyze the break down of tissue proteins and peptides include peptide hydrolases, proteases, endopeptidases, peptidases, and proteinases.
• Venoms that are high in proteinase activity are associated with marked tissue destruction.

Effects of Snake Venom

• In humans, the course of the poisoning is determined by the kind and amount of venom injected; the site where it is deposited; the general health, size, and age of the patient; the kind of treatment.
• Death in humans may occur within less than 1 hour or after several days, with most deaths occurring between 18 and 32 hours.
• Hypotension or shock is the major therapeutic problem in North American crotalid bites.

Snakebite Treatment

• snake venom poisoning is a medical emergency requiring immediate attention
• the venom is a complex mixture of substances of which the proteins contribute the major deleterious properties, and the only adequate antidote is the use of specific or polyspecific antivenom
• not every bite by a venomous snake ends in an envenomation

ANTIVENOM

• Antivenoms have been produced against most medically important snake, spider, scorpion, and marine toxins.
• Animals immunized with venom develop a variety of antibodies to the many antigens in the venom.
• Antivenom consists of venom-specific antisera or antibodies concentrated from immune serum to the venom.
• Antisera contain neutralizing antibodies: one antigen (monospecific) or several antigens (polyspecific).
• Monovalent antivenoms have a high neutralization capacity, which is desirable against the venom of a specific animal.
• Polyvalent antisera are typically used to cover several venoms, such as snakes from a geographic region. Polyvalent preparations usually required higher doses or volumes than monovalent antivenoms.